The invention relates to a method for separating solid reaction products such as SiO.sub.2 and SiC from the molten silicon produced in an arc furnace from the reduction of SiO.sub.2 and carbon.
For an economical utilization of solar energy with solar cells of crystalline silicon, the costs for the production of the silicon must be substantially lowered. The best-known and presently most cost-beneficial method for producing silicon is the carbothermic reduction of quartz in an arc furnace. Such a method may be derived, for example, from the book "Silizium als Halbleiter" by R. Rost, published by Verlag Berliner Union, Stuttgart, pages 18,19, incorporated herein by reference. As a consequence of the highly contaminated starting materials such as quartz, oil coke, charcoal, and coal that are used in this method, the silicon produced only has a purity of 96 to 98.5% and is thus unsuitable for the manufacture of solar cells.
U.S. Pat. No. 4,247,528, incorporated herein by reference, discloses a method for the production of solar cell silicon in an arc furnace wherein high-purity starting substances (SiO.sub.2 and soot) are processed under high-purity conditions. As a result thereof, the boron and phosphorous content and the content of heavy metals are lowered and a purity of 99.9% is achieved; however, contaminants are still contained in the melt in the form of solid reaction products (non-reduced quartz, non-reacted carbon and silicon carbide particles) which complicate a further processing into silicon crystals. A double Czochralski drawing process by means of which all particles are eliminated has proven itself in this regard. The solar cells manufactured from this material have efficiencies greater than 10%. The additional process steps of crystal drawing, however, are expensive and involved.